The present invention relates to a fuel injector for an afterburner of a turbojet engine, more particularly such a fuel injector which improves cooling of the fuel tube.
Afterburners for turbojet engines are well known in the art and have long been utilized as a means to provide additional thrust to the turbojet engine. Typically, afterburners inject fuel into the hot gases emanating from the combustion chamber of the turbojet engine, downstream of the turbine stages. The fuel may be ignited by the elevated temperature of the exhaust gases, or supplemental ignition means may be provided to ignite the fuel/gas mixture.
When the afterburner is activated, fuel passes through one or more generally radially oriented fuel injectors into the afterburner combustion chamber. The fuel passing through the injector also acts as a coolant to lower the temperature of the injector structure, which is subjected to the hot gases from the engine combustion chamber. When the afterburner is not in operation, the fuel injectors are still exposed to the high temperature exhaust gases, but do not receive the benefit of the fuel cooling, since no fuel is passing through the injectors. As a result, coking of the fuel injectors may occur and large thermal shocks may be generated when the afterburner is subsequently activated.
U.S. Pat. No. 4,887,425 discloses a fuel spray bar for an afterburner in which each fuel spray bar has a plurality of fuel tubes extending into the afterburner combustion chamber. The fuel tubes for a particular fuel spray bar each have different lengths and a cooling device is located upstream of the forwardmost fuel tube. The cooling device directs air from a bypass passage of the turbojet engine onto the fuel tubes to control their temperatures. The cooling circuits for this device comprise a number of discharge orifices located opposite the fuel tubes and means to channel the discharged cooling air around the tubes. Such structure requires delicate machining of the parts to ensure that the space between the tubes and the cooling means be uniform over their entire lengths.